A Search for Dark Matter Lines at the Galactic Center with 14 Years of Fermi Data

TL;DR

This study analyzes 14 years of Fermi-LAT gamma-ray data to search for monochromatic lines indicative of dark matter annihilation or decay in the Galactic Center, setting new constraints on dark matter models.

Contribution

It provides the most stringent limits to date on gamma-ray lines from dark matter in the 10 GeV to 2 TeV range using spatial and spectral analysis techniques.

Findings

Constraints on annihilation cross-section: $oxed{ ext{less than } 6 imes 10^{-30} ext{ cm}^3/ ext{s}}$

Constraints on decay lifetime: $oxed{ ext{greater than } 10^{30} ext{s}}$

Line search more sensitive than continuum in many models.

Abstract

Dark matter (DM) in the Milky Way halo may annihilate or decay to photons, producing monochromatic gamma rays. We search for DM-induced spectral lines using 14 years of data from the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope ($\textit{Fermi}$-LAT) between $10\,\mathrm{GeV}$ and $2\,\mathrm{TeV}$ in the inner Milky Way leveraging both the spatial and spectral morphology of an expected signal. We present new constraints as strong as $\langle \sigma v \rangle \lesssim 6\times 10^{-30}\, \mathrm{cm}^3/\mathrm{s}$ for the two-to-two annihilations and $\tau \gtrsim 10^{30}\,\mathrm{s}$ for one-to-two decays, representing leading sensitivity between $10\,\mathrm{GeV}$ and $\sim$$500\,\mathrm{GeV}$. We consider the implications of our line-constraints on the Galactic Center Excess (GCE), which is a previously-observed excess of continuum $\sim$GeV gamma-rays that may be explained by DM annihilation. The Higgs portal and neutralino-like DM scenarios, which have been extensively discussed as possible origins of the GCE, are constrained by our work because of the lack of observed one-loop decays to two photons. More generally, we interpret our null results in a variety of annihilating and decaying DM models, such as neutralinos, gravitinos, and glueballs, showing that in many cases the line search is more powerful than the continuum, despite the continuum annihilation being at tree level.